1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same and, more particularly, a semiconductor device having a capacitor and a method of manufacturing the same.
2. Description of the Prior Art
In the semiconductor memory device, the integration density of the memory cell is increased more and more based on the request for the larger capacity. The memory cell in DRAM consists of the MOS transistor and the capacitor, and the capacitor region is reduced with the higher integration of the memory cell. Then, if the capacitor forming region is reduced, the electrostatic capacity of the capacitor is also reduced, which causes increase in the soft error rate or reduction in the refreshing capability.
Therefore, in order to increase the electrostatic capacity of the capacitor, such a configuration is adopted that either a surface area of the storage electrode constituting the capacitor is increased or material with a high dielectric constant is employed as material of the dielectric film. In order to increase the surface area of the storage electrode, it has been known that a height of the storage electrode is increased, or the storage electrode is formed as a cylindrical shape, or a HSG (Hemispherical Grained Silicon) layer is formed on a surface of the storage electrode.
The increase of the surface area by forming the HSG layer on the surface of the storage electrode is set forth in Patent Application Publication (KOKAI) Hei 11-135759 and Patent Application Publication (KOKAI) Hei 9-186302, for example.
The formation of such HSG layer on the surface of the cylindrical storage electrode has such a merit that the surface area of the storage electrode is increased much more.
However, after the HSG layer is formed on the surface of the cylindrical storage electrode, the hemispherical silicon is ready to come off from the ring like upper surface or the corner portion of the cylindrical storage electrode. Especially, coming-off of the hemispherical silicon occurs remarkably if the HSG layer is cleaned by the chemicals after such HSG layer is formed on the surface of the cylindrical silicon.
For example, as shown in FIG. 1A, a number of hemispherical projections 100 are formed on the uppermost ring-like surface of the storage electrode immediately after the HSG layer is formed on the overall surface of the cylindrical silicon storage electrode. In this case, if the storage electrode is cleaned by use of the liquid chemicals thereafter, a part of the hemispherical projections 100 on the uppermost surface are come off. Thus, as shown in FIG. 1B, coming-off pieces 101 of the hemispherical projections 100 cause the cylindrical storage electrodes 102 and 102 to short-circuit each other.
It is an object of the present invention to provide a semiconductor device having a cylindrical storage electrode in which it is difficult for a silicon projection to come off from an upper surface, and a method of manufacturing the same.
According to the present invention, before the hemispherical grained silicon is formed on the surface of the undoped or low impurity concentration cylindrical or column amorphous silicon film, the impurity is implanted into the uppermost surface of the cylindrical amorphous silicon film with high concentration, e.g., higher than 2xc3x971020 cmxe2x88x923.
According to such condition, the hemispherical grained silicon is extremely difficult to grow on the uppermost surface of the amorphous silicon film, and thus the density of the hemispherical grained silicon can be reduced largely lower than that of the side surfaces (the inner peripheral surface and the outer peripheral surface in the case of the cylindrical shape). The hemispherical grained silicon is formed on the surface by the movement of silicon atoms. Such movement of the silicon atoms is suppressed in the higher impurity concentration portion of the amorphous silicon film.
Such a probability that the hemispherical grained silicon comes off from the corner portion of the uppermost surface of the cylindrical amorphous silicon film can be extremely reduced. Thus, the short circuit between the adjacent silicon films due to the come-off hemispherical grained silicon is avoided.